This invention relates to vacuum pumps, especially to such pumps of the oil-sealed rotary type, and more particularly to mechanisms in these pumps which isolate the pump inlet from the chamber (or whatever) being evacuated by the provision of a certain design of inlet valve.
Rotary vacuum pumps of the type having a vaned rotor rotating in a pump chamber and scaled by means of scaling liquids, normally oils, are well known; these liquids also act as lubricants and coolants for the pump. However, there is a possibility when such pumps are turned off that the oil (or process gas) can contaminate the vacuum chamber or vacuum system associated with the pump.
With such pumps there is a danger of the oil (or its vapors) or the process gas being sucked back into the vacuum system associated with the pump when the pump is turned off. Although this danger can be eliminated by ensuring that all the possible routes into the pump are leak tight, it is often difficult to achieve this readily.
The use of an inlet valve for the pump is known which closes the inlet when the pump is tamed off to prevent the oil (or its vapors) or the process gas from passing out of the inlet to the vacuum system by "suck back".
An inlet valve that can close over the pump inlet is the most direct manner of scaling off the inlet. However, these valves are commonly unreliable, especially if the oil is contaminated by constituents of the substance being pumped, as they are generally operated by a continuous flow of oil past tight diametrical clearances in the valve mechanism which act as a sieve and tend to collect particles of dirt, leading to a seizure of a valve piston or prevention of complete valve closure. Furthermore, such valves also tend to be relatively complicated and therefore expensive to install in the pumps.
The necessary pressure of oil in the pump required for efficient operation is provided by an oil pump associated with the vacuum pump itself.
Commonly the oil pump is contained within the vacuum pump housing and may be driven by the same motor (often by the same shaft rotated by the motor) used to operate the vacuum pump.